package com.juzhi.dvrapp.videoplay.audio;
/*G711A--PCMA*/
public class G711A {
	/** decompress table constants */
	private static short aLawDecompressTable[] = new short[] { -5504, -5248,
			-6016, -5760, -4480, -4224, -4992, -4736, -7552, -7296, -8064,
			-7808, -6528, -6272, -7040, -6784, -2752, -2624, -3008, -2880,
			-2240, -2112, -2496, -2368, -3776, -3648, -4032, -3904, -3264,
			-3136, -3520, -3392, -22016, -20992, -24064, -23040, -17920,
			-16896, -19968, -18944, -30208, -29184, -32256, -31232, -26112,
			-25088, -28160, -27136, -11008, -10496, -12032, -11520, -8960,
			-8448, -9984, -9472, -15104, -14592, -16128, -15616, -13056,
			-12544, -14080, -13568, -344, -328, -376, -360, -280, -264, -312,
			-296, -472, -456, -504, -488, -408, -392, -440, -424, -88, -72,
			-120, -104, -24, -8, -56, -40, -216, -200, -248, -232, -152, -136,
			-184, -168, -1376, -1312, -1504, -1440, -1120, -1056, -1248, -1184,
			-1888, -1824, -2016, -1952, -1632, -1568, -1760, -1696, -688, -656,
			-752, -720, -560, -528, -624, -592, -944, -912, -1008, -976, -816,
			-784, -880, -848, 5504, 5248, 6016, 5760, 4480, 4224, 4992, 4736,
			7552, 7296, 8064, 7808, 6528, 6272, 7040, 6784, 2752, 2624, 3008,
			2880, 2240, 2112, 2496, 2368, 3776, 3648, 4032, 3904, 3264, 3136,
			3520, 3392, 22016, 20992, 24064, 23040, 17920, 16896, 19968, 18944,
			30208, 29184, 32256, 31232, 26112, 25088, 28160, 27136, 11008,
			10496, 12032, 11520, 8960, 8448, 9984, 9472, 15104, 14592, 16128,
			15616, 13056, 12544, 14080, 13568, 344, 328, 376, 360, 280, 264,
			312, 296, 472, 456, 504, 488, 408, 392, 440, 424, 88, 72, 120, 104,
			24, 8, 56, 40, 216, 200, 248, 232, 152, 136, 184, 168, 1376, 1312,
			1504, 1440, 1120, 1056, 1248, 1184, 1888, 1824, 2016, 1952, 1632,
			1568, 1760, 1696, 688, 656, 752, 720, 560, 528, 624, 592, 944, 912,
			1008, 976, 816, 784, 880, 848 };

	private final static int cClip = 32635;
	private static byte aLawCompressTable[] = new byte[] { 1, 1, 2, 2, 3, 3, 3,
			3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
			5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
			6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7,
			7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
			7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
			7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7 };
	
	/**
	* @方法: encode
	* @描述: TODO(压缩函数)
	* @参数 @param src--需要压缩的数据源
	* @参数 @param offset--开始位置
	* @参数 @param len--编译量
	* @参数 @param res--压缩后输出数据
	* @参数 @return
	* @返回 int  压缩后的数据长度
	*/
	public int encode(byte[] src, int offset, int len, byte[] res) {
		int j = offset;
		int count = len / 2;
		short sample = 0;

		for (int i = 0; i < count; i++) {
			sample = (short) (((src[j++] & 0xff) | (src[j++]) << 8));
			res[i] = linearToALawSample(sample);
		}
		return count;
	}

	private byte linearToALawSample(short sample) {
		int sign;
		int exponent;
		int mantissa;
		int s;

		sign = ((~sample) >> 8) & 0x80;
		if (!(sign == 0x80)) {
			sample = (short) -sample;
		}
		if (sample > cClip) {
			sample = cClip;
		}
		if (sample >= 256) {
			exponent = (int) aLawCompressTable[(sample >> 8) & 0x7F];
			mantissa = (sample >> (exponent + 3)) & 0x0F;
			s = (exponent << 4) | mantissa;
		} else {
			s = sample >> 4;
		}
		s ^= (sign ^ 0x55);
		return (byte) s;
	}

	/**
	* @方法: decode
	* @描述: TODO(解压函数)
		* @参数 @param src--需要解压缩的数据源
	* @参数 @param offset--开始位置
	* @参数 @param len--编译量
	* @参数 @param res--解压后的数据
	* @返回 void
	*/
	public void decode(byte[] src, int offset, int len, byte[] res) {
		int j = 0;
		for (int i = 0; i < len; i++) {
			short s = aLawDecompressTable[src[i + offset] & 0xff];
			res[j++] = (byte) s;
			res[j++] = (byte) (s >> 8);
		}
	}
}